The present disclosure relates to semiconductor device manufacturing.
An integrated circuit (IC) is a set of electronic circuits on a single chip of semiconductor material such as silicon. An IC contains core logic devices such as logic gates, flip-flops, multiplexers, and other circuits that perform basic logic functions. Examples of ICs include microprocessors, digital signal processors (DSPs), microcontrollers, application-specific integrated circuits (ASICs), and memory chips. A system on chip (SOC) is an IC that integrates components (e.g., a microprocessor and a memory) of an electronic system on a single chip.
One specific example of a memory that can be included on a chip is a static random access memory (SRAM). A SRAM includes SRAM cells, multiplexing circuitry, and demultiplexing circuitry. A SRAM cell stores a bit of data using the state of a six-transistor memory cell. Multiple SRAM cells (e.g., 8 or 16 cells) that are accessed by the same address form a memory block. A SRAM is manufactured in a logic process for fast speed, low standby power, and simple process flow. A SRAM may be produced using a multiple-gate field effect transistor (e.g., FinFET) process technology.
In an advanced FinFET process technology, the threshold voltage (Vt) of a SRAM transistor is tied to the threshold voltage of a standard Vt (SVT) transistor, and thus the driving current of the SRAM transistor is tied to the driving current of the SVT transistor. For example, in a 16 nm FinFET manufacturing process, the same threshold voltage implant is shared between a SRAM transistor and a SVT transistor. As another example, in a Hi-K Metal Gate manufacturing process, the same work function metal is shared between a SRAM transistor and a SVT transistor. Because the threshold voltage of the SRAM transistor is tied to the threshold voltage of a SVT transistor, adjusting the threshold voltage of the SRAM transistor would require changing the threshold voltage of the SVT transistor. Typically, the SVT transistor is part of a core logic device and changing the threshold voltage of the SVT transistor may affect the timing and functionality of the core logic device.